Solvent fractionation of waxcontaining mixtures



July 22, 1952 E. w. CLARKE 2,604,433

SOLVENT FRACTIONATION OF WAX-CONTAINING MIXTURES Original Filed Sept. 16, 1947 EX TN. SOLVENT Z'M'ADDITIVE INVENTOR. Ecfywzr 7/62 rise W BM? BY m KM HTTEAS'T Patented July 22, 1952 soLvnN'r FRACTIONATION OF WaxooN'rAINING MIXTURES,

Edgar W. Clarke, Laurel Springs, .L, assignor' to The Atlantic Refining Company, Philadeb" phia, Pa, a corporation of Pennsylvania Original application September 16, 1947, Serial No. 774,230. Divided and this application November 5, 1949, Serial No. 125,723

3 Claims. 1

The present invention relates to the treatment of oily waxes, and more particularly to the separation of wax-containing, mixtures into fractions of'higher and lower melting point, using a solvent nitrobenzene and an additive comprising furfural.

This application is a division of copending application Serial Number 774,230, filed September 16, 1947, now Patent No. 2,578,510, and entitled Solvent Fractionation of Wax-Containing Mixtures. I

The present invention is especially applicable to the de-oiling of hydrocarbon waxes containing' not more than about 70% of oil, and to the separation of wax mixtures of low oil content into fractions of diiierent melting point. The process mineral oil, synthetic hydrocarbon oil, shale oi1,

coal, and waxes produced synthetically by the catalytic reaction of hydrocarbons, or waxesjdea rived from the modified Fischer-Tropsch reaction of carbon monoxide and hydrogen. The process of this invention is especially applicable in the separation of wax mixtures containing color bodies ando'il into a higher melting wax fraction of light color and low oil content, and a lower melting wax fraction of darker color and containing most of the oil originally present in the wax mixture.

'In accordance with this invention, a wax-containing mixture is separated into fractions of higher and lower melting point by countercurrently contacting the wax-containing mixture in anextracti'on zone with an extraction solvent and a solvent additive or additives at a temperature such that two liquid phases are formed, one comprising the higher melting wax fraction with minor amounts of solvent and additive, and the other comprising the lower melting wax fraction with major amounts of solvent and'additive, separating the liquid phases from one another, and removing the solvent and additive from each. The extraction solvent and additives employed may have a density greater than that of the wax. tives are partially immiscible with the extraction solvent and are less dense than such solvent or vthewax, the additive or additives will flow countercurrent to the extraction solvent and will appear with that liquid phase comprising the higher meltingwaxfraction. The success of the process However, when the additiveor addidepends upon the controlof the temperature throughout the extraction. zone and .upon the regulation of the proportions of solvent and additive used, and the points of introduction of the wax-containing mixture, the solvent, and the additive into the extraction zone.

The extraction solvent may be defined as an agent which, when intimately mixed with a waxcontaining mixture, forms two liquid phases or layers, one comprising a raffinate phase containingmostly wax of higher melting point than the untreated wax and a portion of the solvent, and the other comprising an extract phasecontaine ing mostly solvent, and Wax of lower melting point than the untreated wax, as well as the major portion of the color bodies and oil originally pres ent in the untreated wax.

The solvent additive may be defined as an agent, used in conjunction with the extraction solvent for the purpose of modifying the characteristics of the extraction solvent. The additive may lower the temperature at which solid wax precipitates, out of the extraction solvent, or it may raise the miscibility temperature of the extraction solvent with the wax. However, the additive chosen for a particular extraction solvent must not exces sively lower the selectivity of the extraction solvent at the temperature of extraction. The extraction solvent may be employed in amounts ranging from 1 to 5 volumes of solvent per volume of untreated wax stock, while the additive or additives may be used in amounts ranging from,0.05 to 1 volume per volume of untreated wax. V The extraction solvents which may be employed inaccordance with the present invention com prise nitrobenzene containing a small amount of fur-fural;

The solvent additive or additives, which are usually employed in amounts constituting not more than by volume of the extraction solvent, comprise furfural.

The process of the present invention maybe carried out in a multi-stage batch countercur rent extraction system or in a continuous cou'n tercurrent extraction system, preferably a tower provided with perforated baffles or containing a packing material'such as-ceramic shapes, tiles, metal wool, or fragments of ceramic-material, glass, pumice, Carborundu'm, or concrete. For

most effective operation, a temperature gradient ismaintained in the system-by means of heating or cooling coils or jackets, the temperature increasing in the direction of fiow of the rafiina-te or higher melting wax fraction.

The present invention may be further understood with reference to the accompanying drawing which illustrates diagrammatically a continuous extraction system suitable for carrying out the process.

Referring to the drawing, a wax-containing mixture is continuously introduced, in liquid condition, into the extraction tower I through valve-controlled pipeZ at a' rate of 100 volumes per hour. An extraction solvent comprising nitrobenzene containing a small amount of furfural is continuously introduced from vessel 3 by means of valve-controlledpipe 4 and manifold into the upper section of the tower below the rafi'inate outlet at a rate of 200 volumes per hour. The first additive comprising furfural is continuously introduced from vessel 5 through valvecontrolled pipe 1 into the extraction tower I below the wax inlet at a rate of volumes per hour. The second additive also comprising furfural is continuously introduced by valvecontrolled pipe 8 into the extraction tower I between the point of introduction of the first additive and the outlet of the extract phase, at a rate of 20 volumes per hour, such second additive being delivered from vessel 9 through pipe I0. An intimate countercurrent contacting of the wax stock, the extraction Solvent, and the additives is efiected in tower I, a temperature gradient being maintained in the tower by means of coils II through which a heatingor cooling medium is circulated as required, the. tempera ture adjacent-the top of the tower being higher than that adjacent the bottom of the tower, the contents of the tower being entirely in the liquid phase. The wax stock, being subjected to the action of the solvent and additives, is caused to separate by solvent action into two fractions, the higher melting fraction wax passing upwardly through the tower together with a minor amount of dissolved extraction solvent and additive, and being withdrawn therefrom above the level of the dotted line l2 representing the higher melting wax phase relatively free of entrained, immiscible solvent and additive. The raflinate phase comprising the higher melting wax and dissolved solvent and additive is passed from the top of tower I through valve-controlled pipe I3 into a vacuum evaporator or still Il'wherein the solvent, and additive is removed from the higher melting -wax by vaporization, the solvent and additive vapors passing through pipe I5 into fractionating tower I6 provided with a reboiler or heating coil I1, while the higher melting wax is drawn from the bottom of evaporator I4- and delivered by valve-controlled pipe I8 into storage vessel I9. 'Such wax fraction was white in color, and had a substantially higher melting point and a lower oil content than the original waxy mixture.-

The extract phase comprising the lowermelting wax fraction, color bodies, oil, and the major portion of the extraction solvent and additives is withdrawn from the lower section of tower I beneath the level of the dotted line 20 representing the extract phase relatively free of, entrained, higher melting wax. The extract phase is delivered by valve-controlled pipe 2| into a vacuum'evaporator or still 22 wherein the solvent and additives are vaporized from the lower melting wax, the latter being drawn from the bottom of the evaporator and passed by valve-controlled pipe 23 to storage vessel 24. The lower melting wax was brown in color and had a substantially lower melting point and a higher oil content than the original waxy mixture,

by means of valve-controlled pipe 27.

The solvent and additive vapors are passed from the top of evaporator 22 through pipe 25 into fractionating tower I6, wherein such vapors together with those introduced through pipe I5, are fractionated, the extraction solvent, i. e., nitrobenzene, being drawn from the bottom of the tower as a liquid and returned by means of pipe 26 to the solvent storage vessel 3 for reuse. The desired small amount, for example, 5% 'to 10% of furfural is incorporated in the nitrobenzene by introducing the furfural from vessel 6 The additive, i. e., furfural, separated from the nitrobenzene by fractionation in tower I6 is taken overhead as vapor by pipe 28, condensed in condenser 29 and returned by pipes 30 and 3| to vessels 6 and 9, respectively. A portion of the vapor stream may be diverted through valvecontrolled pipe 32, condensed in condenser 33, and the condensate returned as reflux to the top of tower I6 by pipe 34.

Depending upon the temperature of operation, the first additive may be introduced somewhat above the point of introduction of the liquefied waxy stock, for example, by means of valve-controlled pipe 35 rather than through valve-controlled pipe I, in which case the second additive may be admitted through either or both of valve-controlled pipes I and 8 below the point of introduction of the wax stock. In general, the raifinate wax phase withdrawn from the extraction tower will contain from 5% to 25% of solvent and additive, while the extract wax phase will contain from 55% to of solvent and additive.

In the event that the extraction is to be carried out in a multi-stage batch countercurrent system, for example, a 4-stage system using the solvent and additives specifically set forth above, the wax stock would be introduced into the first stage extractor, the extraction solvent comprising nitrobenzene and a small amount of furfural would be introduced into the fourth stage extractor, and the first additive, i. e., furfural, would be introduced into the first stage extractor. The second additive, e. g., furfural, would be introduced into the second stage extractor. The extract phase is withdrawn from th first stage extractor, while the rafiinate phase would be removed from the fourth stage extractor. The temperature would increase progressively from the first stage to the fourth stage, using the waxy stock, solvent, and additives described hereinabove. It is to be understood, of course, that the quantities and composition of the solvent and of the additives may be varied within certain Extraction Solvent 1st Additive 2nd Additive nitrobenzene 10% iuriural 2 =I= furfural 0.2 :l: furfural 0.2 d:

0.4 vols. 0.05 vols. vols.

The present invention is further illustratedby the following example, which, however, is not to be construed as limiting the scope thereof:

(1) A slack wax having a melting point of 113 F. and an oil content of 24.2% by weight was extracted in a system similar to that shown in the accompanying drawing, the extraction solventco'mprising 2 volumes of nitrobenzene containing be term-a1; the first additive comprising 0.2 volume of furfural, and the second additive comprising 0.2 volumeof ;furf-ural.,g'I;'he

v slack waxwas introduced intotower l by pipe 2, the solvent by pipe d-and manifold 5, the first additive by pipe 1 and the second additive 'by pipe 8. Thetemperature in theextraction-tower table:

Charge Rafiinate Extract Wax Wax Wax Weight Yield per cent 100 59. 6 40. 1 Melting Point F 113. l 127. 4 91. 0 Oil Content, Weight per 7 cent 24. 2 0. 5 60. 3 Refractive Index at 176 F; 1. 43625 1. 42890 1. 45332 A. P. Gravity 40. 5 42. 5 34. 3 Color Brown White Dark Brown Firmness. Nil Good Nil Tackiness, Poor Good Poor Plasticity. Too Soft Good Too Soft Fiber Length Short Long Short Flexibility Poor Moderate Poor Where the extraction operation is conducted in a tower, it has been found that a tower having a height of about 40 feet and a diameter of from the bottom thereof, or approximately the distance from the bottom of the tower. The extraction solvent is charged just above the upper level of the packing, for example, 3 to 4 feet from the top of the tower. The firstadditive may be introduced adjacent the point of introduction 'of the wax stock, for example, 2 ,feet above or below the wax inlet. The secondadditive is introduced approximately 2 feet: below the point of introduction of the first additive. These values'may be altered somewhat, depending upon I the tower design, the solvent and additives used,

and the temperatures maintained at various levels in the tower. The raffinate phase iswithdrawn from thetop of the tower, and the extract phase from the bottom thereof, the extraction solvent being more dense than the wax stock. I claim: I l. The method of separating a wax-containing mixture into fractions of higher and lower melting point, which comprises countercurrently contacting said wax-containing mixture in an extraction zone with an extraction solvent and solvent additives at a temperature such that two immiscible liquid phases are formed, one comthespoint of withdrawal of the lower melting waxfraction, the-solvent comprising 1.6 to:2.4 vol umes of riitrobenzene containing a small amount offurfural per volume of wax-containing 'mixture, the first additive comprising 0.15170 0.25 volume of furfural per volume of 'wax contain-r ing mixture; 'and the secondadditive compris- I ing 0.l5 to 025 volume of furfural per volume prising the higher melting wax fraction containing solvent and additives,and the other comprising solvent and additives and the lower melt,- ing wax fraction, separating the phases from one another, and removing the solvent and additives from each, the solvent being introduced into the extraction zone near the point of withdrawal of the higher melting wax fraction, the first additive being introduced adjacent the point of introduction of the wax-containing mixture, and

of wax 'containing mixture.

2. The method of separating a wax-containing mixture into fractions of higher and lower melting point, which comprises countercurrently contacting said wax-containing mixture in an extraction zone with an extraction solvent.

and solvent additives at'a temperature such that two immiscible liquid phases are formed, one comprising the higher melting Wax fraction with minor amounts of solvent and additives, and the other comprising the lower melting wax fraction with major amounts of solvent and additives, separating the phases from one anlower melting wax fraction, .the solvent com-' prising 1.6 to 2.4 volumes of nitrobenzene containing 10% of furfural per volume of wax-containing mixture, the first additive comprising 0.15 to 0.25 volume of furfural per volume of wax-containing mixture, and the second additive comprising 0.15 to 0.25 volume of furfural per volume of wax-containing mixture.

' 3. In a method of separating a wax-containing mixture into fractions of higher and lower melting point, wherein the wax-containing mixture is contacted in an extraction zone with an extraction solvent and solvent additives at a temperature above the melting point but below the temperature of complete miscibility of the mixture, the steps which comprise introducing 1 volume of liquefied wax-containing mixture into the extraction zone at a point intermediate the points of withdrawal of the higher and lower melting waxes including the solvent and additive; introducing 1.6 to 2.4 volumes of extraction solvent comprising nitrobenzene containing 10% of furfural at a point adjacent the point of withdrawal of the higher melting wax fraction including solvent and additive, but intermediate said point of withdrawal and the point of introduction of the liquefied wax-containing mixture, and introducing 0.15 to 0.25 volume of an 1 additive. comprising furfural intermediate the point of introduction of the liquefied waxcontaining mixture and the point of withdrawal of the lower melting wax fraction including solvent and additive, introducing 0.15 to 0.25 volume of an additive comprising furfural at a point intermediate the point of introduction of the first additive and the point of withdrawal of the lower melting wax fraction including solvent and additive, effecting countercurrent contact between the liquefied wax-containing mixture and the solvent and additives at a temperature such that two immiscible liquid phases are formed, one phase comprising the higher melting wax fraction containing minor amounts of solvent and additives, and the other liquid phase comprising the lower; melting wax fraction and. 1 REFERENCES CITED major amounts of Solvent and additives" the I The following references are of record' in the peraturein the extraction zone increasing in. the 1 7 r t direction of flow of the higher melting wax fracof t tion, separately withdrawing the respectivegliquid 5 7' 1 UNITED T E phases from the extraction 'zone, and;removing Nunaber I 7 Namei Date, the solvent and additives from each. 7 12,017,432. Bahlke Oct. 15,.1935 1 2,063,369 Diggs et a]. Dec. 8, ,1936

' 2,138,833 Brown et a1. Dec. 6, 193a v 10 2,160,930 1 Whiteley et a1. June 6, 1939 

1. THE METHOD OF SEPARATING A WAX-CONTAINING MIXTURE INTO FRACTIONS OF HIGHR AND LOWER MELTING POINT, WHICH COMPRISES COUNTERCURRENTLY CONTACTING SAID WAX-CONTAINING MIXTURE IN AN EXTRACTION ZONE WITH AN EXTRACTION SOLVENT AND SOLVENT ADDITIVES AT A TEMPERATURE SUCH THAT TWO IMMISCIBLE LIQUID PHASES ARE FORMED, ONE COMPRISING THE HIGHER MELTING WAX FRACTION CONTAINING SOLVENT AND ADDITIVES, AND THE OTHER COMPRISING SOLVENT AND ADDITIVES AND THE LOWER MELTING WAX FRACTION, SEPARATING THE PHASES FROM ONE ANOTHER, AND REMOVING THE SOLVENT AND ADDITIVES FROM EACH, THE SOLVENT BEING INTRODUCED INTO THE EXTRACTION ZONE NEAR THE POINT OF WITHDRAWAL OF THE HIGHER MELTING WAX FRACTION, THE FIRST ADDITIVE BEING INTRODUCED ADJACENT THE POINT OF INTRODUCTION OF THE WAX-CONTAINING MIXTURE, AND THE SECOND ADDITIVE BEING INTRODUCED BETWEEN THE 